1 answer

2

... because the spelling out of numbers is not a rule of grammar. It is, however, a matter of style, and Grammarly does not check for style. Complicating matters, the guidance provided by the various major style guides is not unanimous on the topic.

While the "rule" you cite is often taught in elementary and high school, most major American, academic style guides -- the Chicago Manual of Style, the Modern Language Association, the American Pyschological Association -- endorse a different general rule:

Numbers 0-99 are generally spelled out -- twenty-seven, forty-eight, and seventy-one; but 117 and 243

Numbers that can be expressed in two words are generally spelled out -- one hundred, two thousand, and twenty thousand; but 21,000.

Numbers that begin a sentence are always spelled out (no exceptions).

But isn't your sentence "wrong" in any case? No. The style guides all emphasize consistency over slavish adherence to the rule. When a passage (typically a paragraph or two in length) contains numbers that cannot be spelled out -- say 1,216 -- then all numbers in the passage should be written as numerals. It is this "consistency" guideline that bedevils software.

Thank you for your assistance, however, I am confused by the "but 117 and 243" as part of "Numbers 0-99 are generally spelled out -- twenty-seven, forty-eight, and seventy-one; but 117 and 243"Please clarify. Thank you very much.

Styles guides often show examples where the rule is true and then where the rule is false. So in my examples, I spelled out twenty-seven because it falls within the 0-99 "rule" -- but used numbers for 117 because it is greater than 99 and thus falls outside the 0-99 rule.